AUTO TRANSFORMER - it is a one winding transformer. This winding is used to provide primary and secondary winding turns and these two are not electrically isolated as in normal 2 winding transformer. The transformation ratio of auto transformer is near to Unity for the same voltage ratio and capacity, the auto Transformer require less amount of copper. The auto transformer may be step up or step down transformer.
If the number of primary turns is N1 and Number of secondary turns is N2 and K is transformation ratio then (N1/N2) = K. If N1 is greater than N2, so the auto transformer is a step down transformer, otherwise it is step up transformer. In auto transformer power is transferred through two modes ie. Inductively and conductivity. Copper is saved in auto transformer because auto transformer has only one winding so it consumes less amount of copper. The volume of copper depends upon the area of cross section and length of conductor.
